0 Replies
      Latest reply on Mar 21, 2020 2:01 AM by steveluoxin
      steveluoxin Level 1 Level 1 (0 points)
        1. Use NSFetchedResultsController as the data source for UITableView. It is created with main context (persistentContainer.viewContext).
        2. Execute batch delete using background context
        3. Merge changes into main context to update UI. (This is the problem. It freezes main thread).


        Here are the related codes:


        let mainContext = persistentContainer.viewContext
        let taskContext = persistentContainer.newBackgroundContext()
        taskContext.performAndWait {  
          let fetchRequest = NSFetchRequest(entityName: "MyItem")
          fetchRequest.includesPropertyValues = false
          let batchDeleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
          batchDeleteRequest.resultType = .resultTypeObjectIDs
          do {
          let result = try taskContext.execute(batchDeleteRequest) as? NSBatchDeleteResult
          let objectIDArray = result?.result as? [NSManagedObjectID]
          let changes = [NSDeletedObjectsKey : objectIDArray]
          /****below line of codes is the problem, it blocks main thread****/ 
          NSManagedObjectContext.mergeChanges(fromRemoteContextSave: changes as [AnyHashable : Any], into: [mainContext])
          } catch {
          print("Error batch delete items: \(error.localizedDescription)")

        Is there any way to avoid blocking main thread in this situation? Thanks